This disclosure is related to polyalkylstyrene-polysiloxane block copolymers, methods of manufacture thereof and to articles comprising the same. In particular, this disclosure is related to polyalkylstyrene-polysiloxane block copolymers used for improved nano lithography patterning.
Modern electronic devices are moving toward utilization of structures that have a periodicity of less than 40 nanometers. The ability to shrink the size and spacing of various features on a given substrate (e.g., gates in field effect transistors) is currently limited by the wavelength of light used to expose photoresists (i.e., 193 nm). These limitations create a significant challenge for the fabrication of features having a critical dimension (CD) of <50 nm.
Block copolymers have been proposed as one solution to formation of patterns with periodicity of less than 40 nanometers. Block copolymers form self-assembled nanostructures in order to reduce the free energy of the system. Nanostructures are those having average largest widths or thicknesses of less than 100 nanometers. This self-assembly produces periodic structures as a result of the reduction in free energy. The periodic structures can be in the form of domains, lamellae or cylinders. Because of these structures, thin films of block copolymers provide spatial chemical contrast at the nanometer-scale and, therefore, they have been used as an alternative low-cost nano-patterning material for generating periodic nanoscale structures.
Many attempts have been made to develop copolymers and processes for patterning. FIGS. 1A and 1B depict examples of lamella forming block copolymers that are disposed upon a substrate. The block copolymer comprises a block A and a block B that are reactively bonded to each other and that are immiscible with each other. The alignment of lamellae domains can be either parallel (FIG. 1A) or perpendicular (FIG. 1B) to the surface of a substrate surface upon which they are disposed. The perpendicularly oriented lamellae provide nanoscale line patterns, while there is no surface pattern created by parallel oriented lamellae.
Where lamellae form parallel to the plane of the substrate, one lamellar phase forms a first layer at the surface of the substrate (in the x-y plane of the substrate), and another lamellar phase forms an overlying parallel layer on the first layer, so that no lateral patterns of microdomains and no lateral chemical contrast form when viewing the film along the perpendicular (z) axis. When lamellae form perpendicular to the surface, the perpendicularly oriented lamellae provide nanoscale line patterns. Cylinder forming block copolymers, on the other hand, provide nanoscale line patterns when the cylinders form parallel to the surface and hole or post patterns when the cylinders form perpendicular to the surface. Therefore, to form a useful pattern, control of the orientation of the self-assembled microdomains in the block copolymer is desirable.
The block copolymer is desirably annealed with heat (in the presence of an optional solvent), which allows for microphase separation of the polymer blocks A and B at a temperature above the glass transition temperature and below the order to disorder transition temperature. The annealed film can then be further developed by a suitable method such as immersion in a solvent/developer or by reactive ion etching which preferentially removes one polymer block and not the other to reveal a pattern that is commensurate with the positioning of one of the blocks in the copolymer.
The use of conventional block copolymers present difficulties in orientation control and long range ordering during the self assembly process. Diblock copolymers of poly(styrene) and poly(dimethylsiloxane) (PS-b-PDMS) offer promise for application in the patterning of nanoscale dimensions (especially sub-45 nm) using directed self assembly techniques. The etch selectivity between the polystyrene and poly(dimethylsiloxane) domains makes these materials useful for patterning. Conventional wisdom in the art, however, is that the use of PS-b-PDMS block copolymers in such operations cannot effectively be thermally annealed due to the large incompatibility between the polystyrene and polydimethylsiloxane blocks. This is especially apparent in PS-b-PDMS materials that display a spacing of 30 nm or larger. For any block copolymer system, as the interdomain spacing increases, the material becomes more difficult to anneal to low defectivity. Accordingly, those in the art have developed a variety of alternative techniques for processing of block copolymers like poly(styrene)-b-poly(dimethylsiloxane) block copolymers. For example, in U.S. Patent Publication No. 2011/0272381; Millward, et al., disclose a solvent annealing method for processing diblock copolymer films such as poly(styrene)-b-poly(dimethylsiloxane).
On the other hand, block copolymers comprising polystyrene and poly(2-vinyl pyridine) (PS-b-P2VP) can be annealed to low defectivity at 30 nm pitch under thermal annealing processes, but these materials lack inherent etch selectivity between the component blocks. Accordingly, metal staining of the P2VP is required to impart etch selectivity to enable pattern transfer with these materials. This process swells the poly(2-vinyl pyridine) domain, resulting in damage to the morphology that is manifested by an unacceptable line edge roughness (LER) for commercial use.
Notwithstanding, there remains a need for new copolymer compositions for use in patterning substrates. In particular, there remains a need for new copolymer compositions that enable patterning on intermediate length scales of 20 to 40 nm and that preferably exhibit a fast annealing profile with low defect formation.
It is therefore desirable to find block copolymers that contain polystyrene and polydimethylsiloxane that can generate self-assembled films having domain sizes of less than 25 nanometers with a periodicity of less than 50 nanometers. Additionally, it is desirable to find block copolymers that contain polystyrene and polydimethylsiloxane that can deliver low defects at 50 nm or less pitch under thermal annealing processes without a metal staining process, as this would save additional expensive processing steps and should lead to lower (better) line width roughness.